It has only been in the last few years that many digitization projects have taken a serious approach to digital preservation. In that time CD-R has quickly become the most common media for preserving digital images, with more recently a move towards DVD-R due to the additional space that it offers. The popularity of both these media is largely due to their ease of use and low cost. However during this time, there has been a steady flow of worrying reports of 'lost data' or 'unreadable disks', which has lead to the reliability of laser-burnt media being questioned. Much of this worry has been centered on the choice of disc manufacturer and the construction method used to create the disc. Of course a project should always buy the best and most reliable discs it can find, however, it should be remembered that loss of digital data stored on CD-R and DVD-R is far more likely to be caused by bad writing (burning) or storage rather than by badly manufactured discs in the first place. CD-R and DVD-R can provide reliable back up at a reasonable cost as long as great care and attention is paid to burning them and storing them correctly.
To ensure reliability of discs in the long-term, it is imperative to follow a few 'best practice' steps when burning CD-R and DVD-R discs.Start by establishing a Digital Preservation Strategy to plan for future migration of your digital images.
Remember the choice of preservation media is only one small part of the whole Digital Preservation Strategy; make sure you plan to use all known best practice from the very outset of the project. One of the first and most important issues to consider is "who is going to 'own' this valuable resource long after your project has finished?" This ownership will come with responsibilities to protect and look after the data (whether it is on CD-R or any other media). This will require an ongoing budget - part of which will be needed to cover future migration to new storage media.
Whilst CD-R has, over the last few years, been the de facto choice for preservation, DVD-R is fast becoming a preferable alternative. DVD-R discs hold up to 4.7 GB of data compared to a CD-R 700Mb and there are an increasing number of recordable DVD drives available (which also read/write CD-R). If your project is in the early stages, or you have not yet started archiving to CD-R, you may want to look at DVD-R as an option.
Looking beyond DVD, one possible contender for the next-generation standard is the Blue-ray Disc currently under development, which promises a data capacity of 27 GB. Of course it is never easy to predict what the next standard is going to be (in any part of the digitization process), but it is fairly safe to assume that technology will move on, so it is essential to be prepared for future migration. See TASI Advice Document Establishing a Digital Preservation Strategy for further advice on preservation strategies.
